The present invention relates to a motor driver suitable for driving a brushless DC motor built in, e.g., an air conditioner, a water heater, an air cleaner, and an information apparatus such as a copying machine, a printer and the like. More particularly, relates it to an efficient motor driver through which alternate current changing sequentially runs, thereby reducing torque ripples, vibrations and noises in activating the motor. Sine-wave current is preferred to the alternate current.
DC brushless motors have been widely used as driving motors built in, e.g., an air conditioner and an information apparatus including a copying machine, a printer and the like because of their advantages such as a long service-life, high reliability, and easiness of speed control.
FIG. 21 is a circuit diagram of a conventional motor driver. FIG. 22 shows waveforms at respective sections of the driver with respect to a rotating angle (electric angle) of the motor when a voltage of a rectangular waveform is applied to the motor driving coils of the driver.
As shown in FIG. 21, in a driver of a brushless DC motor (hereinafter simply referred to as a motor), a rotor position is detected by a plurality of position detectors 901, 903 and 905 comprising a Hall effect device. Three-phase distributor 890 receives position signals Hu, Hv and Hw, and outputs three-phase distribution signals U0, V0 and W0 to pulse-width modulating (PWM) comparator 840. At this time, signals U0, V0 and W0 shape in one-step signals different from each other by 120 degree in electrical angles as shown in FIG. 22. Comparator 840 outputs a signal which controls, via gate driver 830, six switches constituting power-feeder 820 sequentially to be turned ON or OFF. Power supplied to three-phase coils 811, 813 and 815 is thus switched in sequence responsive to a rotor position, thereby spinning the motor.
A voltagexe2x80x94applied between a coil end of phase U and neutral point Nxe2x80x94shapes in a rectangular waveform signal as shown at U-N in FIG. 2. Signals in rectangular waveforms similar to this are applied to phase V and phase W. Changing a current in the three-phase coils causes sharp ON-OFF switches responsive to the rectangular waveform signals. As a result, coils are vibrated, mechanical noises and electrical noises are produced.
A motor driver, which lowers noises and electric noises discussed above, is disclosed in Japanese Patent No. 2658085. This motor driver uses detection output from a detecting element which detects main magnetic-field for driving, and an address signal formed of pulses having frequencies higher than that of the output of the detecting element, whereby a driving waveform stored in a memory is read out for driving the motor. This structure eliminates a frequency generator (FG) and a detecting element (PG) to be simplified. The FG has a constant number of pulses per rotation of the rotor as well as a frequency varying responsive to an r.p.m. of the rotor, and the PG detects magnetic flux from a permanent magnet disposed at given places on the outer wall of the rotor.
The conventional motor driver discussed above, however, requires a memory storing a predetermined driving waveform and a digital-analog (D/A) converter which reads out the driving waveform (digital signal) before converting the digital signal into an analog signal for driving the motor. Therefore, the conventional motor driver needs a complicated circuit.
Further, in the conventional motor driver discussed above, the driving waveform with respect to a rotational position of the rotor, namely, a voltage waveform applied to the coils of respective phases, is uniquely determined by digital-signal data stored in the memory discussed above. Thus, in the case where the driver drives a motor having a rather large inductance, e.g., a stator iron core is wounded with coils, a phase delay of current of respective phases with respect to the voltages applied to the respective phases becomes larger when the driving waveform is applied to the respective phases. As a result, efficiency of the motor is lowered.
The present invention addresses the problem discussed above, and aims to provide a simply structured and efficient motor-driver which can reduce torque ripples, vibrations and noises of a motor.
The motor driver of the present invention comprises the following elements:
(a) driving coils for three phases;
(b) a power feeder, connected to a dc power supply, for powering the coils of the respective phases;
(c) a position detector for detecting a mover position with respect to the respective phases;
(d) a positional signal interpolator, disposed for at least one of the phases, for dividing one cycle in electrical angles of a positional signal of at least one phase into 3nxc3x974 cycles (xe2x80x9cnxe2x80x9d is an integer equal to or more than xe2x80x9c1xe2x80x9d), where the positional signal is produced by an output from the position detector; and
(e) a driving-waveform generator for receiving a dividing address-signal from the interpolator, producing a step-waveform for each of three phases where the step-waveform has a voltage level (not exceeding the steps of 3n+1) preset corresponding to respective addresses of the address signal, and outputting the step-waveforms in voltages.
A driving signal for each of the respective phases, corresponding to the step-waveforms for three phases, is applied to the power feeder, thereby driving the motor with an alternate current which changes respective phase-coils sequentially.
The motor driver of the present invention can be equipped with three positional-signal interpolators, three driving-waveform generators for the three phases individually, in other words, the motor driver comprises the following elements:
A motor driver comprising the following elements:
(a) driving coils for three phases;
(b) a power feeder, connected to a dc power supply, for powering the coils of the respective phases;
(c) a position detector for detecting a mover position with respect to the respective phases;
(d) positional signal interpolators, disposed for each of the phases, for dividing one cycle in electrical angles of respective phase-positional-signals produced by outputs from the position detector into 3nxc3x974 cycles (xe2x80x9cnxe2x80x9d is an integer equal to or more than xe2x80x9c1xe2x80x9d); and
(e) driving-waveform generators, disposed for each of the respective phases, for receiving a dividing address-signal from each of the interpolators, producing a step-waveform for each of three phases where the step-waveform has a voltage level (not exceeding the steps of 3n+1) preset corresponding to respective addresses of the address signal, and outputting the step-waveforms voltages.
A driving signal for each of respective phases, corresponding to each step of the step-waveforms, is applied to the power feeder, thereby driving the motor with an alternate current which changes respective phase-coils sequentially.
This structure allows the motor driver not only to reduce torque ripples at starting a motor, vibrations and noises, but also to drive the motor in an efficient manner.